Method of xerographic development



March 5, 1963 c. J. CLAUS 3,080,251

METHOD OF XEROGRAPHIC DEVELOPMENT Filed. March 13, 1958' YDROPHILICCOLLOID YDROPHOBIC RESIN ATTORNEY been limited to heat OI-SOIVCI1 vapor,although-other methods such as United Se ates "3,080,251 -METI-ID' OFXEROGRAPHIC DEVELOPMENT -"CarlJ.- Claus, Rochester,fN.Y., assignortoXerox 1 Corporation, ar-corporationzof New.Y.ork :.1Filed Mar; .13,.1958, :Ser; No. 721,201

.This; invention. relates. in gener.a1 to. electrostatic. vrecording andr in: particular to. materials and methods for :Inthe art ofxerography,itis usual to forman. elec- Ltrostaticimage on a suitable .insulatingorphotoconduc- =.tive insulating surface and to develop this image, orin .other words'make it visible, by presenting to thesurface ranelectroscopic marking material. In the. usual embodiv.ments .ofxerographyzthe electrostatic image is formed on a photoconductiveinsulating surface by charging the surface and exposing it to an imageof light and shadow .to is dissipated bearing surface with such as,forexample, Because of requirements xerographic develop- In thesepermanently other surfaceas shall be desired for a final imagesupportqmember. Existing fixing operations have generally fusing the.image material by means of lacquer spraying, overlaying and the likehave occasionally been employed.

An. object of the. present invention is to provide new imagematerialsand methods for electrostatic recording wherein an. electrostatic imagemay be developed and Another object of the invention is to provide a newelectroscopic image developing material for-xerographic recording which.image material is capable of being deposited in response to an.electrostatic charge. pattern and subsequently madevisible .on'the imagesupport surface bymeans ofpressure.

Anadditional-object of .the invention is to provide anew xerographicdeveloping material comprisingancn- .capsulatedmarking materialincludinga liquid .dropletof a color .forming composition within ashellhaving. surface .triboelectric. properties. suitable for electrostatic.deposi- .tion.

A' further. object is to provide new. materials ..and

..methodsfor xerographywherein an encapsulateddevelop- ..ingmaterialiscombined with an active photoconductor .to produce apermanent, visible image.

.Additional. objects .of the..invention will in part .be obvious. andwillin -part become apparent from-the following specification anddrawing in which:

..The FIGUREisa diagrammatic viewof a developer powderparticle-according to one form ofthe. invention. 1 l Ithas. recently...been found thatsuitable liquid, ma- =.Yl'.6l2l3.lS-. can..bel formed.into ..an extremely finelydivided 'dry composition by separateencapsulation of appropriate ..liquid droplets within red a hydrophilicshell. "For example,

.I in U.S.' Patent 2,800,458, there is disclosed a manufacchemical orphysical reagent.

tured' preparation. of oil-containing capsulesbf hardened gelatin. Suchcompositions have numerous usesin pres- .sure recording arts..Unfortunately, it has been found Ithat "these compositions areessentially unsatisfactory for electrostatic recording because of'theirextreme variability in triboelectric properties depending on humidity inthe atmosphere. It has nowbeen found that image forming powders ofproper triboelectric properties can'be pro- .duced by encapsulating aliquid droplet ,of a suitable color forming material within ahydrophilic coating such ..as gelatinv or the like, and in turnencapsulating the hydrophilic material within a tough hydrophobic resincoating. In particular, outer coatings of the polystyrenefamilyincluding polymerized styrene, polystyrene homologues and mixturesand copolymers'thereof, and resins of the acrylic esters acrylic amideand methacrylic esters and amides and mixtures of copolymers thereof, aswell as mixtures of styrene and acrylic resins may be produced onhydrophilic capsules by immersion in polymer solutions followed bydrying 0r evaporation of the solvent to produce developer materials forXerography.

The new developer powder composition includes essentially three separatephases or components, such as, for example a liquid droplet 10 encasedin a hydrophilic coating 11, in turn within a hydrophobic resin coating12. Theliquid composition comprises essentially an oil base dyeintermediate capable of forming, by chemical or physical reactions, ahighly colored material, or other composition in liquid form capable ofreacting to produce a permanent color visible on a support sheet suchas, for example, a sheet of paper or the like having a photoconductivecoating thereon. Suitable oil bases include oils and other,non-polarfluids generally not miscible with water but such as forexample waxes, mineral oils, animal oils and the like, aswell asvegetable oils such as olive oil, castor oil, and the like. Desirably,an oil composition may include asolution of a resin material in asuitable solvent such as for example a hydrocarbon solvent together withthe col-or forming material.

An essential active agent included in the liquid droplet within theencapsulated particle is the color forming compound, optionally initself substantially colorless, capable of producing a highly coloredmaterial upon release by pressure rupture of the capsule in contact witha suitable According to a presently preferred embodiment of theinvention the reagent for reaction with such colorless color formingcompound. is an acidic adsorbent photoconductive material capable ofinclusion in an insulating resin binder to produce a photoconductiveinsulating layer. Thus, for example, photoconductive, insulators such aszinc oxide, mercuric iodide,

Zinc sulfide, cadmium sulfide, cadmium dioxide, and the like, may beincluded in insulating resinbinders such as siliconeresins,acrylicresins, polystyrene and the like, as

. is known in the art, to produce image forming xerographic layers. Suchlayers generally act as acidic type adsorb- ..entsandaccordingly arereactive with manycolor form- 'color .forming compounds may be includedin the encapsulated liquid droplet: Crystal violet lactone (3,3-bis-('4- dimethylaminophenyl) 6-dimethylamino-phthalide), malachite greenlactone (3,3 bis (4 dimethylaminophenyl)-phthalide), dimethyl malachitegreen lactone (3, 3 his (4 -dimethylamino-3-methylphenyl)-phthalide),Michiers hydrol (bis-(4-dimethylaminophenyl)-c-arbinol), Michlers hydrolmethyl ether (bis-(4-dimethylarninophenyl)-methyl methyl ether), diethylcrystal violet lactone (3,3bis-(4-dimethylamino-3-ethylphenyl)-6-dimethylamino-phthalide), andmono-methylamino crystal violet lactone (3 ,3-bis l-methylaminophenyl)-6-methylamino-phthalide) The oil composition is contained within ahydrophilic colloid material such as, for example, gelatin casing or thelike and may be formed into an encapsulated powder with materials andmethods disclosed in Green et al. U.S. Patent 2,800,457. Suitableencapsulating material includes gelatin, hydrophilic cellulose materialssuch as hydrophilic cellulose esters and ethers, gums and the like.

Suitable capsules such as, for example, capsules as disclosed in theGreen et al. patent may be coated with a resin to form a xerographicdeveloper composition. As a preferred procedure, the gelatin capsulematerial is dipped or immersed into a solution of a mixture ofpolystyrene and polystyrene homologues dissolved in toluene, xylene, ora similar non-aqueous organic solvent. The mixture is suitably agitatedand dried by spray drying or the like to produce capsules substantiallyuniformly coated with the polystyrene type resin. According to apresently preferred procedure a polystyrene type material believed toconsist of a polymerized mixture of styrene and styrene homologues andavailable under the name Piccolastic Dl is employed. This resin isdissolved in xylene, and the capsules are immersed in the solution.Excess liquid is filtered off and the coated capsules air dried withoccasional mixing. Alternatively the capsules may be dried according toconventional spray drying procedures.

In one procedure for producing a xerographic developer the polystyrenecoated capsule powder is mixed with a granular bead-like carriermaterial such as disclosed in Walkup Patent U.S. 2,816,551, generally inthe amount of 1% of the powder composition and 99% of the carriercomposition. The mixed developer material is useful in xerographic imagedevelopment as, for example, by cascading the mixture across the surfaceof the electrostatic image bearing xerographic plate or across thesurface of an electrostatic image bearing insulating surface.

Alternatively, the powder material may be employed for image developmentby blowing it into an air cloud and directing the air cloud to the imagesurface, by mixing the powder material with a ferromagnetic material andmagnetically conveying the mixture into brushing contact with the imagesurface, or by dusting the powder material into a brush such as, forexample, a fur brush and brushing the image surface. Other imagedevelopment methods may include dispersing the powder in an inert liquidand applying a liquid suspension by dipping or immersing or by pouringthe liquid suspension across the image surface or the like.

Upon image development in any of these methods it has been found that apowder image is formed on the image bearing surface. The image may bemade permanently visible and afiixed to the original image surface bymeans of pressure rollers or the like, or may be transferred to anadjacent surface and subsequently afiixed to such an adjacent surface.Thus, for example, a xerographic image may be formed on a seleniumcoated metal plate or drum by applying an electrostatic charge to theselenium surface. The image may be developed by the methods of theinvention and transferred to a piece of coated paper placed in contactwith the image bearing selenium plate or drum by means of coronadischarge or the like and the image permanently affixed to the paper bymeans of pressure rollers. According to a presently preferred embodimentof the invention the electric image is directly formed on a paper backedphotoconductor such Al as zinc oxide in an insulating silicone,polystyrene, acrylic resin or the like and is developed and fixed insitu.

As an illustrative example of the present invention an encapsulatedmaterial may be prepared of one of the color formers, such as crystalviolet lactone. This color former is encased in a hardened gelatinencapsulating wall coated with a polystyrene layer as describedhereinbefore. In a preferred embodiment of the invention the tonercomposition produced by the methods described is mixed with iron filingsin a ratio of about 20 parts iron filings to 1 part toner by weight andthe mixture employed as a developer according to the method of YoungU.S. 2,786,- 441. A suitable zinc oxide containing xerographic papercompatible with the toner composition is available under the nameLectroX Paper, from the Haloid Company, Rochester, New York, andincludes a photoconductive layer having as an active agent zinc oxidecapable of imparting photoconductivity to the layer and capable of reacting with the active agent Within the encapsulated droplet. Anelectrostatic image is formed on the coated paper by electricallycharging the paper and exposing the charged paper to an image of lightand shadow to be recorded. The mixture of iron filings and tonermaterial is then brushed across the surface of the xerographic paperhearing an electrostatic image, and the toner deposits in imageconfiguration. The resulting powder deposit can be made highly coloredand permanently visible on the zinc oxide layer by rupturing theencapsulating walls, for example, bynpassing the image bearing paperthrough hard pressure ro ers.

The present invention permits the use for xerography of a wide varietyof color forming materials without regard to the triboelectricproperties of such color formers. There may be employed, moreover,carbon black and other carbonaceous materials and other colorintensifying materials in the liquid droplet or in the particle shellitself in additou to the color formers dispersed or dissolved in oilbase. The xerographic developer compositions prepared with such markingmaterials are independent of the triboelectric characteristics of thecomposition of the droplet itself or of the encapsulating materials inwhich the color forming materials are mutually encased. It has beenfound that desired triboelectricity and humidity resistance can beimparted to the composition by polymerized styrene and polymerizedacrylic resins and that such resins may be employed without regard tothe nature of the color former or the oil base.

What is claimed is:

1. The method of xerography comprising forming an electrostatic imagecomprising information to be recorded on a composite photoconductivelayer wherein zinc oxide is the photoconductive constitutent by thecombined action of light and electric field acting on said layer,developing the image bearing layer by electrostatically depositingthereon a xerographic toner composition consisting of particlestriboelectrically adapted independently of ambient humidity and in asize range for use in conjunction With a xerographic carrier to form atoner carrier system for developing xerographic images, said particlesconsisting of an inner core of a substantially colorless color formingliquid capable of reacting with an acidic adsorbent to form a highlycolored material and encapsulated in a rupturable hardened hydrophiliccolloid shell, and an outer rupturable shell of hydrophobic resin coatedon said colloid shell, said hydrophobic resin being triboelectricallyadapted for use with a xerographic carrier and selected from the groupconsisting of polystyrene resins and polyacrylic resins, and rupturingsaid particles on the photoconductor layer to cause a color formingreaction between the liquid in said particles and the zinc oxidephotoconductor.

2. The method of claim 1 in which said color forming liquid includes asan active ingredient thereof a material selected from the groupconsisting of crystal violet lactone (3,3bis-(4-dimethyl-aminophenyl)-6-dimethyl- References Cited in the file ofthis patent UNITED STATES PATENTS 2,512,192 Yen et al. June 20, 19502,712,507 Green July 5, 1955 2,730,456 Green et a1. Jan. 10, 19562,735,784 Greig et a1 Feb. 21, 1956 6 Greig Feb. 21, 1956 Walkup Mar. 5,1957 Rheinfrank et a1. Apr. 9, 1957 Green July 23, 1957 Mayer Mar. 10,1959 Green et a1 Sept. 20, 1960 FOREIGN PATENTS Great Britain of 1910Great Britain Aug. 10, 1955 France Nov. 9, 1955 Great Britain Oct. 31,1956 OTHER REFERENCES Young st 211.: Electrofax, R.C.A. Review, December1954, pp. 469 to 484, vol. XV, No.4.

1. THE METHOD OF XEROGRAPHY COMPRISING FORMING AN ELECTROSTATIC IMAGECOMPRISING INFORMATION TO BE RECORDED ON A COMPOSITE PHOTOCONDUCTIVELAYER WHEREIN ZINC OXIDE IS THE PHOTOCONDUCTIVE CONSTITUTENT BY THECOMBINED ACTION OF LIGHT AND ELECTRIC FIELD ACTING ON SAID LAYER,DEVELOPING THE IMAGE BEARING LAYER BY ELECTROSTATICALLY DEPOSITINGTHEREON A XEROGRAPHIC TONER COMPOSITION CONSISTING OF PARTICLESTRIBOELECTRICALLY ADAPTED INDEPENDENTLY OF AMBIENT HUMIDITY AND IN ASIZE RANGE FOR USE IN CONJUNCTION WITH A XEROGRAPHIC CARRIER TO FORM ATONER CARRIER SYSTEM FOR DEVELOPING XEROGRAPHIC IMAGES, SAID PARTICLESCONSISTING OF AN INNER CORE FO A SUBSTANTIALLY COLORLESS COLOR FORMINGLIQUID CAPABLE OF REACTING WITH AN ACIDIC ADSORBENT TO FORM A HIGHLYCOLORED MATERIAL AND ENCAPSULATED IN A RUPTURABLE HARDENED HYDROPHILICCOLLOID SHELL, AND AN OUTER RUPTURABLE SHELL OF HYDROPHOBIC RESIN COATEDON SAID COLLOID SHELL, SAID HYDROPHOBIC RESIN BEING TRIBOELECTRICALLYADAPTED FOR USE WITH A XEROGRAPHIC CARRIER AND SELECTED FROM THE GROUPCONSISTING OF POLYSTYRENE RESINS AND POLYACRYLIC RESINS, AND RUPTURINGSAID PARTICLES ON THE PHOTOCONDUCTOR LAYER TO CAUSE A COLOR FORMINGREACTION BETWEEN THE LIQUID IN SAID PARTICLES AND THE ZINC OXIDEPHOTOCONDUCTOR.